Add test case for 6g bug: result variable does not hide the

package name in the scope.

R=r
DELTA=12  (12 added, 0 deleted, 0 changed)
OCL=15913
CL=15926

test/bugs/bug107.go

+// errchk $G $D/$F.go
+
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+import ip "ip"
+func f() (ip int) {
+     // In the next line "ip" should refer to the result variable, not
+     // to the package.
+     v := ip.ParseIP("")	// ERROR "undefined"
+     return 0
+}

test/golden.out

@@ -169,6 +169,9 @@ pc: xxx
 =========== bugs/bug104.go
 BUG: errchk: command succeeded unexpectedly:  6g bugs/bug104.go
 
+=========== bugs/bug107.go
+BUG: errchk: command succeeded unexpectedly:  6g bugs/bug107.go
+
 =========== fixedbugs/bug016.go
 fixedbugs/bug016.go:7: overflow converting constant to <uint32>UINT32